1. Field of the Invention
This invention relates in general to aircraft and in particular to model aircraft components constructed with twin wall fluted plastic sheet material.
2. Description of Prior Art
In order to provide background information so that the invention may be completely understood and appreciated in its proper context, reference may be made to a number of prior art publications as follows:
1) Cub Instructions, Carl Goldberg Models 4734 W. Chicago Ave, Chicago, Ill. 60651 pub 2077 1-585. PA1 2) CoroStar 40 Construction Manual U.S. AirCore 4576 Clair Chennault, Hangar 7, Dallas Tex., 75248 Part Number USA11141. PA1 3) Sig Catalog #51 Sig Manufacturing Company, Inc. 401-7 Front St., Montezuma Iowa 50171 PA1 4) Gentle Lady Instructions. Carl Goldberg Models 4734 W. Chicago Ave, Chicago Ill. 60651 pub 2-680
Model aircraft have traditionally been constructed of lightweight wood (such as balsa) used to form a frame, covered with a film which forms the skin (Ref 1). Recent models have been constructed of vacuum formed plastic sheet laminated over foamed plastic cores. More recent models have been constructed of extruded twin wall fluted plastic sheet. (Ref 2), This material is extruded of various plastic compounds. Polypropylene based compounds have been most effective in that they can be formulated to provide a material which is stiff enough to form airfoils, fuselages, and flight control surfaces, and remain flexible enough to absorb most crashes without exceeding the elastic limit of the material, thus avoiding permanent damage.
Construction of model aircraft with twin wall fluted plastic sheet is much less tedious than construction with wooden frame and sheet skin, and results in models which are much more durable than those constructed by other methods. Twin wall fluted plastic sheet construction presents some unique problems. Traditional hinges of thin plastic sheet or leaf and pin construction (Ref 3 p 92) can be used for control surfaces, but are no easier to install in these new aircraft than in those of traditional construction. Model aircraft hinges have also been constructed from heat shrinkable plastic film covering material which forms the skin of model aircraft with traditional wood frames (Ref 4 p10). These hinges have the advantage of being continuous along the entire length of the control surface, and low in marginal cost, since they are typically constructed of excess covering material. Continuous hinges exhibit less drag than multiple hinges due to the smoothed airflow from the fixed surface over the control surface. Twin wall fluted plastic sheet for model aircraft is not a suitable surface for bonding heat shrinkable film covering material, since the temperatures required exceed the softening point of the polypropylene. A continuous hinge suitable for model aircraft constructed with twin wall fluted plastic sheet is needed.
Early control systems for aircraft provided for distorting or warping wings or other flight surfaces to effect changes in aircraft attitude. There techniques were quickly replaced with separate control surfaces hinged to fixed flight surfaces, since hinged surfaces provided more precise and stable control systems. Until the present invention, the control surface was a separate and distinct piece from its accompanying fixed flight surface, requiring construction of multiple pieces which were joined with hinges. Construction from a single piece, yet resulting in an independent, hinged control surface had yet to be achieved.
Landing gear of model aircraft have, in the past, been constructed of two pieces of spring steel (Ref 1) and affixed to the model's fuselage. The vertical portion of the gear is inserted into slots or holes in the fuselage to provide longitudinal stability to the gear. Aircraft constructed of twin wall fluted sheet require slots or holes in added wooden parts to accommodate these vertical portions of the gear in order to prevent tearing the plastic during hard landings. Another method of providing longitudinal stability is needed.
Another traditional landing gear is made of flat material (Reference 3, page 58). This gear is made of sheet metal or molded plastic. It provides longitudinal stability with its wide mounting surface, and spring action from the material of construction. It is typically heavier and more expensive than landing gear made from formed spring wire.
Both wire and flat gear have another shortcoming, in that they provide no damping. Gear constructed of concentric cylinders, fluids, and controlled orifices provide damping through viscous friction, but are expensive to construct. Damping in the landing gear prevents the aircraft from bouncing as a result of hard landing. It is much easier to control the path of an aircraft if initial contact with the landing surface is not interrupted by bouncing.
Biplanes must have a method to secure the two wings at the proper angles to the fuselage and tail surfaces, provide the proper separation between the wings, and, in replications of early biplanes, provide clearance from the top of the fuselage to the bottom of the top wing. Traditionally, wooden frame members and wires have performed this function. It is tedious to construct model aircraft in this manner. Since models made with extruded fluted plastic sheet typically have little or no internal structure, simple struts are needed for these biplanes. Similarly, monoplanes with wing elevated from the fuselage require struts to attach the wing to the fuselage. Struts which attach wings to fuselages are sometimes referred to as cabanes. We use the term "strut" to include both functions.
Electro-mechanical actuators, known as "servos" for radio controlled model aircraft are typically mounted near the center of the model for reasons of balance. If, for example, the servos which control the rudder and elevator were mounted in the tail, additional weight would need to be added to the nose for proper balance. A lightweight mechanical linkage, or "pushrod" is required to transfer force and motion from servos to control surfaces. Likewise, in a control line aircraft, a linkage is required from the center of pull, near the center of the wing, to the elevator. Pushrods are often fabricated from lightweight wood, wire, and string as shown in Reference 1. More recently, pushrod assemblies, consisting of an outer sleeve which houses an inner rod have been manufactured by various suppliers. One such example is shown in Reference 3, page 101 or 152. A lower cost, lighter weight pushrod system is needed for aircraft constructed from fluted plastic sheet.
Whatever the precise merits, features and advantages of the above cited references, none of them achieves or fulfills the purposes of the aircraft components of the present invention.